On Saturday, it came to light that Sonnen tested positive again in blood and urine samples given at another random drug test administered on June 5 in Portland, Ore.

Both tests were administered at the behest of the Nevada Athletic Commission because Sonnen at the time had been scheduled to fight at UFC 175 on July 5 in Las Vegas. NAC chairman Francisco Aguilar confirmed the second drug test to MMAWeekly.com following an initial report by MMAFighting.com.

It’s not that surprising that Sonnen would test positive again less than two weeks after the first failed test. It is surprising, though, that two of the four substances he tested positive for on the Portland-administered drug test were different than those the first test showed.

What he didn’t voluntarily admit to, and what didn’t show up on the May 24 test results, were human growth hormone (hGH) and recombinant human erythropoietin (EPO). Both are performance-enhancing substances that are prohibited by the World Anti-Doping Agency, which is the standard the NAC follows.

More commonly known for its use in professional cycling by the likes of Lance Armstrong and numerous others, EPO stimulates red blood cell production in the body, which increases the amount of oxygen that blood can carry to muscles. This stimulation increases endurance and recovery.

“hGH is known to act on many aspects of cellular metabolism and is also necessary for skeletal growth in humans,” according to WADA’s description of the substance. “The major role of hGH in body growth is to stimulate the liver and other tissues to secrete insulin-like growth factor (IGF-1). IGF-1 stimulates production of cartilage cells, resulting in bone growth and also plays a key role in muscle and organ growth.”

As with the first failed drug test in Las Vegas, Sonnen appears to be saying that he was prescribed medications that also caused the second failed test in Portland.

“Yes, the Commission is aware of other prescribed medications I was taking and I will not challenge their allegations,” he told MMAFighting on Saturday. “I will cooperate with the Commission and look forward to having a dialogue about how fighters who transition off TRT can avoid violating any rules.”

In the wake of the first failed test, Sonnen announced his retirement from mixed martial arts and the NAC temporarily suspended him pending a full disciplinary hearing at the commission’s next meeting, which is slated for July 23 in Las Vegas.